uicontextmenu not rendering reliably

I'm manually showing a uicontextmenu in response to a button press:

%In the button press callback ...
p = getpixelposition(current_button);
set(obj.context_menu,'Visible','on','Position',p(1:2))

However, the context menu does not show up every time I press the button. I have multiple buttons and after I press a couple it seems to show up every time. Also, it shows up reliably for some buttons and rarely for other buttons (until I press the more reliable buttons). Adding drawnow() seems to help ...

My question is, is anyone aware of issues associated with the uicontextmenu rendering? Are there known workarounds to get reliable rendering? Is drawnow() an intended solution? If so, why?

I'm running Mac OS Sierra with 2017a.